The term "used motor oil" is used herein to mean crank case oil from motor vehicles such as, for example, cars, trucks and locomotives, as well as gear oils, automatic transmission fluids and other functional fluids in which the major constituent is an oil of lubricating viscosity. This term does not, however, mean used industrial oils which are blended to specific requirements for use in non-motor vehicle applications in industrial plants or power producing plants.
The term "synthetic crude oil" is used herein to mean any crude oil, regardless of source, other than natural crude petroleum. Synthetic crude oils include oils prepared from naturally occurring bitumen deposits, even though the sources are natural liquids, as well as synthetic hydrocarbon and halosubstituted hydrocarbon oils, alkylene oxide polymers, mono- and dicarboxylic acid esters, synthetic silicon-based oils, etc., all as further discussed below. Synthetic crude oils are useful, for example, in the preparation of lubricants, and normally liquid fuels such as gasoline, kerosene, jet fuel and fuel oil. Processes for the synthesis of synthetic crude oil include liquefication of coal, destructive distillation of kerogen or coal, and extraction or hydrogenation of organic matter in coke liquids, coal tars, tar sands or bitumen deposits, as well as organic synthesis reactions.
Although new reserves of petroleum are from time to time being found, it is generally believed that during the next twenty years new discoveries on a world wide basis will no more than balance the depletion. In the meantime the energy needs for both developing and the developed countries will continue to increase. One approach to this problem has been to encourage better utilization of present supplies, which includes an estimated one billion gallons of used motor oil that is drained, dumped or burned each year in the United States of America. These oils have generally been used as engine crank case lubricants, transmission and gear oils and the like. Used motor oils commonly contain various additives such as detergents, antioxidants, corrosion inhibitors, and extreme pressure additives which are necessary for satisfactory performance, in addition to solid and liquid contaminants, some of which result from oxidation of the oil itself, and generally water and gasoline. Much of this used motor oil could be recovered and reused if it were collected and if it could be effectively reprocessed. Instead, as much as one-third of this used motor oil is indiscriminately dumped, contaminating both land and water. Much of the used motor oil is burned and this too contributes to pollution by releasing metallic oxides from additives in the oil into the atmosphere.
Most existing reclaiming plants for rerefining oil use sulfuric acid to coagulate as an acid sludge the ash and polar components in used oil. This procedure, followed by treatment with alkaline solutions to neutralize the acid, water washing, active clay decolorizing, stripping and filtration yields a lube stock suited to reuse as a low grade motor oil or as a grease base. The poor yield of rerefined oil and environmental problems of disposal of acid sludge and clay make such a reclaiming process a marginal operation at best.
Various alternative approaches have been proposed for reclaiming used motor oil. Propane extraction prior to acid treatment has been reported as reducing the amount of acid and clay required but the yield of recovered oil remains at only about 65% and plant investment costs are much higher. Vacuum distillation has been suggested and work has been done on hydrotreating of distilled oil to lube stock. This latter process leaves a high ash residue and serious problems in fouling of heat exchanger and fractionation equipment has been encountered. Solvent extraction process have been proposed for reclaiming used lubricating oils, but the volume of solvent required has generally been at least equal to the volume of oil being treated and more often at least two to three times the volume of such oil, thus leading to high equipment costs and solvent recovery problems.
A number of processes for reclaiming used oil have been described in the patent literature. For example, U.S. Pat. No. 3,919,076 describes a process for rerefining used automotive lubricating oil that includes the steps of first purifying the oil of debris, dehydrating the oil, then mixing the oil with 1-15 times the volume of such oil of a solvent selected from the group consisting of ethane, propane, butane, pentane, hexane and mixtures thereof, the preferred solvent being propane. The patentee indicates that a special scrubber is used to removed heavy metal particulates from the combustion gases and then the oil-solvent mix is stripped, subjected to vacuum distillation, hydrogenation, another stripping process and filtering. U.S. Pat. No. 3,930,988 describes a process for reclaiming used motor oil by a series of treatments of such oil that includes mixing the oil with ammonium sulfate and/or ammonium bisulfate under conditions that react the sulfate or bisulfate with metal-containing compounds present in the used oil to precipitate contaminants from the oil. The patentee indicates that an optional step of further treating the oil under hydrogenation conditions can be employed to remove additional contaminants and produce a low sh oil product. U.S. Pat. No. 4,021,333 describes a process for rerefining oil by the steps of distilling used oil to remove a forecut having a viscosity substantially less than that of lubricating oil, continuing the distillation to recover a distillate having substantially the viscosity of lubricating oil, extracting impurities from the distillate of the foregoing step with an organic liquid extractant, and removing the organic liquid and impurities dissolved therein from the distillate. U.S. Pat. No. 4,028,226 describes a process for rerefining used oil by the steps of diluting the used oil with a water-soluble polar diluent, removing a major amount of the polar diluent from the solution by addition of water and removal of the resulting aqueous phase, and removing the balance of the polar diluent from the oil. The patentee indicates that useful diluents are the lower alkanols and lower alkanones. U.S. Pat. Nos. 4,073,719 and 4,073,720 describe methods for reclaiming used oil that include the use of a solvent for dissolving the oil and precipitating metal compounds and oxidation products from the oil as sludge. The solvent that is described as being preferred consists of a mixture of isopropyl alcohol, methylethyl ketone and n-butyl alcohol. The solvent-to-used-lubricating-oil ratio is indicated to be in the range of about 8 to about 3 parts solvent to one part oil. U.S. Pat. No. 4,287,049 describes a process for reclaiming used lubricating oil by the steps of contacting the used oil with an aqueous solution of an ammonium salt treating agent in the presence of a polyhydroxy compound at conditions of temperature and pressure sufficient to allow reaction of the treating agent with ash-forming contaminants of the oil thereby producing a precipitate of reacted contaminants, removing a major portion of water and light hydrocarbon components from the reaction mixture, and separating an oil phase from the precipitate by filtration.
A major problem with most reclaiming procedures is the requirement for removing or reducing the level of contaminants, particularly metallic contaminants, to sufficient levels to permit hydrogenation of the reclaimed oil. Most hydrogenation procedures require the use of costly catalyst which can be poisoned by unacceptable levels of such contaminants. Removal or reduction to acceptable levels of such contaminants is essential to the viability of such hydrogenation procedures.
Another approach to this problem has been to encourage the development of alternate fuel and lubricant sources, the most abundant of which are shale oil and coal. The term "shale oil" is a convenient expression used to cover a wide range of fine-grained sedimentary rocks most of which do not contain oil as such, but an organic material believed to be derived mainly from aquatic organisms. The organic constituent of shale oil is called kerogen. Kerogen can be converted to synthetic crude oil by destructive distillation by heating to high temperatures (usually over 900.degree. F.) in a retort. Retorting processes can be divided into three groups: (1) surface retorting, (2) true in situ retorting, and (3) modified in situ retorting. For surface retorting, the shale oil is mined either from the surface by strip mining or underground by room and pillar mining. The rock is then crushed and transported to the retorting vessel. True in situ retorting takes place underground with no mining of the shale. The shale must be fractured by hydraulic pressure, by explosives, or by other means. Modified in situ processes involve some mining to provide a void volume into which the remaining shale can be blasted.
Although most synthetic crude oils derived from shale oil contain less sulfur than Middle Eastern crudes, they contain more nitrogen than typical crudes. For example, synthetic crude oils derived from Green River shale oil usually contains about 1.3-2.2% nitrogen compared to 0.3% for typical petroleum crudes. Nearly all of this nitrogen must be removed prior to conventional refining. A metal contaminant that causes concern in synthetic crude oils derived from shale oil is arsenic. Another metal that can cause problems is iron. Some of the iron may be present as fines; however, up to 70 ppm iron can pass through a 0.45-micron filter and may be bonded in organic compounds. Additionally, nickel, and shale rock particles (known as "fines" or "ash") are potential sources of processing problems. These impurities must be removed prior to transporting synthetic crude oil in common carrier pipelines and prior to refining.
The liquefication of coal for producing synthetic crude oil is of particular significance due to the abundant deposits of coal that are available, particularly in the United States. The major differences between coal and petroleum are the ratio of hydrogen to carbon and the ash content. Coal has an atomic hydrogen to carbon ratio of about 0.8, while the ratio for oil is of the order of about 1.8. Coal has an ash content that can be as high as about 15%, whereas oil seldom has over a few tenths of a percent. The problem, then, in coal liquefication is to increase the hydrogen content of the material and to eliminate the ash. Coal liquefication processes can be grouped into three general categories; pyrolysis, extraction-hydrogenation, and indirect liquefication. In pyrolysis, coal is heated to a temperature at which it begins to decompose and gives off liquids and gases, leaving behind a carbonaceous solid called char. The liquids in gases are higher in hydrogen content than the original coal, while the char is lower in hydrogen. In the extraction-hydrogenation process, hydrogen is added to the coal by a number of different methods, and smaller amounts are rejected. In indirect liquefication, large amounts of hydrogen are added and large amounts of carbon in the form of carbon dioxide are removed. With each type of liquefication, the removal of contaminants, particulaly metallic contaminants, from the resulting synthetic crude oil is essential prior to refining it.
It would be advantageous to provide a process for treating used motor oil and synthetic crude oil to remove undesired contaminants, particularly undesired nitrogen-containing materials and metallic contaminants, sufficiently to permit further processing of such used motor oil (e.g., hydrogenation) and synthetic crude oil (e.g., conventional refining).